1. Field of the Invention
This invention relates to pistons and in particular to a relatively lightweight two-stage piston for multiple stage reciprocating compressors and related equipment.
2. Description of the Prior Art
As is well known in the art, in a typical reciprocating compressor the mechanical losses and deleterious vibrations associated with the reciprocating mass of the pistons can be significantly reduced by reducing the mass of the pistons. However, due to the material strength and fatigue properties generally required to such pistons, the pistons heretofore in use have usually been fabricated from relatively heavy castings and the like. This has been particularly the case with two-stage pistons where pressure loads on two separate piston faces must be carried through a common connection to the connecting rod driving the piston.
In recent years, lightweight composite structures have been employed in a variety of applications where high strength and lightweight constructions are particularly desirable. For example U.S. Pat. Nos. 4,306,489 and 4,450,610 both show pistons for internal combustion engines formed of metal and plastic composites. As can be seen in those patents, both of those designs call for bonding a metal or ceramic cap or cover onto a plastic core to form their respective pistons. However, neither of those patents address the load distribution problems encountered in two-stage pistons where the pressure loads from two separate piston faces must be transfered through the piston to a common connection with the connecting rod.
As indicated in the foregoing, in the past it has generally been necessary to fabricated two-stage pistons from relatively heavy metal castings due to the load distribution problems typical of that type of piston. Thus, while a variety of composite designs have been used for single-stage pistons such as those shown in the patents noted above, weight and vibration has continued to be an on-going problem in the design and fabrication of compressors incorporating two-stage pistons.